1 /* SPDX-License-Identifier: GPL-2.0 */ 2 /* 3 * fs-verity: read-only file-based authenticity protection 4 * 5 * Copyright 2019 Google LLC 6 */ 7 8 #ifndef _FSVERITY_PRIVATE_H 9 #define _FSVERITY_PRIVATE_H 10 11 #ifdef CONFIG_FS_VERITY_DEBUG 12 #define DEBUG 13 #endif 14 15 #define pr_fmt(fmt) "fs-verity: " fmt 16 17 #include <crypto/sha.h> 18 #include <linux/fsverity.h> 19 #include <linux/mempool.h> 20 21 struct ahash_request; 22 23 /* 24 * Implementation limit: maximum depth of the Merkle tree. For now 8 is plenty; 25 * it's enough for over U64_MAX bytes of data using SHA-256 and 4K blocks. 26 */ 27 #define FS_VERITY_MAX_LEVELS 8 28 29 /* 30 * Largest digest size among all hash algorithms supported by fs-verity. 31 * Currently assumed to be <= size of fsverity_descriptor::root_hash. 32 */ 33 #define FS_VERITY_MAX_DIGEST_SIZE SHA512_DIGEST_SIZE 34 35 /* A hash algorithm supported by fs-verity */ 36 struct fsverity_hash_alg { 37 struct crypto_ahash *tfm; /* hash tfm, allocated on demand */ 38 const char *name; /* crypto API name, e.g. sha256 */ 39 unsigned int digest_size; /* digest size in bytes, e.g. 32 for SHA-256 */ 40 unsigned int block_size; /* block size in bytes, e.g. 64 for SHA-256 */ 41 mempool_t req_pool; /* mempool with a preallocated hash request */ 42 }; 43 44 /* Merkle tree parameters: hash algorithm, initial hash state, and topology */ 45 struct merkle_tree_params { 46 struct fsverity_hash_alg *hash_alg; /* the hash algorithm */ 47 const u8 *hashstate; /* initial hash state or NULL */ 48 unsigned int digest_size; /* same as hash_alg->digest_size */ 49 unsigned int block_size; /* size of data and tree blocks */ 50 unsigned int hashes_per_block; /* number of hashes per tree block */ 51 unsigned int log_blocksize; /* log2(block_size) */ 52 unsigned int log_arity; /* log2(hashes_per_block) */ 53 unsigned int num_levels; /* number of levels in Merkle tree */ 54 u64 tree_size; /* Merkle tree size in bytes */ 55 unsigned long level0_blocks; /* number of blocks in tree level 0 */ 56 57 /* 58 * Starting block index for each tree level, ordered from leaf level (0) 59 * to root level ('num_levels - 1') 60 */ 61 u64 level_start[FS_VERITY_MAX_LEVELS]; 62 }; 63 64 /** 65 * fsverity_info - cached verity metadata for an inode 66 * 67 * When a verity file is first opened, an instance of this struct is allocated 68 * and stored in ->i_verity_info; it remains until the inode is evicted. It 69 * caches information about the Merkle tree that's needed to efficiently verify 70 * data read from the file. It also caches the file measurement. The Merkle 71 * tree pages themselves are not cached here, but the filesystem may cache them. 72 */ 73 struct fsverity_info { 74 struct merkle_tree_params tree_params; 75 u8 root_hash[FS_VERITY_MAX_DIGEST_SIZE]; 76 u8 measurement[FS_VERITY_MAX_DIGEST_SIZE]; 77 const struct inode *inode; 78 }; 79 80 /* 81 * Merkle tree properties. The file measurement is the hash of this structure 82 * excluding the signature and with the sig_size field set to 0. 83 */ 84 struct fsverity_descriptor { 85 __u8 version; /* must be 1 */ 86 __u8 hash_algorithm; /* Merkle tree hash algorithm */ 87 __u8 log_blocksize; /* log2 of size of data and tree blocks */ 88 __u8 salt_size; /* size of salt in bytes; 0 if none */ 89 __le32 sig_size; /* size of signature in bytes; 0 if none */ 90 __le64 data_size; /* size of file the Merkle tree is built over */ 91 __u8 root_hash[64]; /* Merkle tree root hash */ 92 __u8 salt[32]; /* salt prepended to each hashed block */ 93 __u8 __reserved[144]; /* must be 0's */ 94 __u8 signature[]; /* optional PKCS#7 signature */ 95 }; 96 97 /* Arbitrary limit to bound the kmalloc() size. Can be changed. */ 98 #define FS_VERITY_MAX_DESCRIPTOR_SIZE 16384 99 100 #define FS_VERITY_MAX_SIGNATURE_SIZE (FS_VERITY_MAX_DESCRIPTOR_SIZE - \ 101 sizeof(struct fsverity_descriptor)) 102 103 /* 104 * Format in which verity file measurements are signed. This is the same as 105 * 'struct fsverity_digest', except here some magic bytes are prepended to 106 * provide some context about what is being signed in case the same key is used 107 * for non-fsverity purposes, and here the fields have fixed endianness. 108 */ 109 struct fsverity_signed_digest { 110 char magic[8]; /* must be "FSVerity" */ 111 __le16 digest_algorithm; 112 __le16 digest_size; 113 __u8 digest[]; 114 }; 115 116 /* hash_algs.c */ 117 118 extern struct fsverity_hash_alg fsverity_hash_algs[]; 119 120 struct fsverity_hash_alg *fsverity_get_hash_alg(const struct inode *inode, 121 unsigned int num); 122 struct ahash_request *fsverity_alloc_hash_request(struct fsverity_hash_alg *alg, 123 gfp_t gfp_flags); 124 void fsverity_free_hash_request(struct fsverity_hash_alg *alg, 125 struct ahash_request *req); 126 const u8 *fsverity_prepare_hash_state(struct fsverity_hash_alg *alg, 127 const u8 *salt, size_t salt_size); 128 int fsverity_hash_page(const struct merkle_tree_params *params, 129 const struct inode *inode, 130 struct ahash_request *req, struct page *page, u8 *out); 131 int fsverity_hash_buffer(struct fsverity_hash_alg *alg, 132 const void *data, size_t size, u8 *out); 133 void __init fsverity_check_hash_algs(void); 134 135 /* init.c */ 136 137 extern void __printf(3, 4) __cold 138 fsverity_msg(const struct inode *inode, const char *level, 139 const char *fmt, ...); 140 141 #define fsverity_warn(inode, fmt, ...) \ 142 fsverity_msg((inode), KERN_WARNING, fmt, ##__VA_ARGS__) 143 #define fsverity_err(inode, fmt, ...) \ 144 fsverity_msg((inode), KERN_ERR, fmt, ##__VA_ARGS__) 145 146 /* open.c */ 147 148 int fsverity_init_merkle_tree_params(struct merkle_tree_params *params, 149 const struct inode *inode, 150 unsigned int hash_algorithm, 151 unsigned int log_blocksize, 152 const u8 *salt, size_t salt_size); 153 154 struct fsverity_info *fsverity_create_info(const struct inode *inode, 155 void *desc, size_t desc_size); 156 157 void fsverity_set_info(struct inode *inode, struct fsverity_info *vi); 158 159 void fsverity_free_info(struct fsverity_info *vi); 160 161 int __init fsverity_init_info_cache(void); 162 void __init fsverity_exit_info_cache(void); 163 164 /* signature.c */ 165 166 #ifdef CONFIG_FS_VERITY_BUILTIN_SIGNATURES 167 int fsverity_verify_signature(const struct fsverity_info *vi, 168 const struct fsverity_descriptor *desc, 169 size_t desc_size); 170 171 int __init fsverity_init_signature(void); 172 #else /* !CONFIG_FS_VERITY_BUILTIN_SIGNATURES */ 173 static inline int 174 fsverity_verify_signature(const struct fsverity_info *vi, 175 const struct fsverity_descriptor *desc, 176 size_t desc_size) 177 { 178 return 0; 179 } 180 181 static inline int fsverity_init_signature(void) 182 { 183 return 0; 184 } 185 #endif /* !CONFIG_FS_VERITY_BUILTIN_SIGNATURES */ 186 187 /* verify.c */ 188 189 int __init fsverity_init_workqueue(void); 190 void __init fsverity_exit_workqueue(void); 191 192 #endif /* _FSVERITY_PRIVATE_H */ 193